Digital broadcast networks enable the unidirectional transmission of data such as audio, video, subtitling text, applications, etc. In broadcast networks, there is typically no return channel from the receiver to the transmitter and thus adaptive techniques cannot be appropriately employed. At present, there are several families of digital broadcast standards around the world. For instance, in Europe, Digital Video Broadcasting (DVB) standards have been adopted. In general, these standards define the physical layer and the data link layer of the broadcast distribution system. The definition of the physical and data link layer depends on the transport medium, which can be for instance a satellite, cable, or terrestrial channel. Correspondingly, the family of DVB standards includes DVB-S and DVB-S2 for satellite transmission, DVB-C and DVB-C2 for cable transmission, DVB-T and DVB-T2 for terrestrial transmission, and DVB-H for terrestrial transmission to handheld devices.
The recent terrestrial digital broadcast standard DVB-T2 is a successor version of the widely used DVB-T standard in the same way as DVB-S2 and DVB-C2 are the second generation replacements of the first generation counterparts DVB-S and DVB-C. The specifications of the two standards for terrestrial transmission, namely the DVB-T2 standard and the DVB-T standard, can be found in Non-Patent Literature 1 and Non-Patent Literature 2, respectively. Further details and remaining DVB specifications can be found in Non-Patent Literature 3. Other than the DVB-T standard, the DVB-T2 standard introduces, for instance, the concept of physical layer pipes (PLP), provides new forward error correction schemes, modulation constellations, larger Orthogonal Frequency Division Multiplexing (OFDM) symbol sizes and more pilot configurations.
The concept of physical layer pipes allows multiple parallel data streams to be multiplexed at the physical layer. The processing for the multiple data streams may be configured separately by means of selecting, for example, a forward error correction (FEC) coding rate, modulation constellation size, interleaving length and other physical layer parameters. The separate configurability of the physical layer pipes enables the provision of different robustness levels for each individual physical layer pipe. In digital broadcasting systems that use physical layer pipes, each service (program) can be transmitted in its own physical layer pipe. This enables reducing the amount of data that must be demodulated at the receiver when assuming that only one service is consumed at a time, since the receiver only needs to demodulate the data carried in the corresponding physical layer pipe. The physical layer pipe processing includes an input processing, a forward error correction (FEC) encoding, a constellation mapping, and an interleaving. Within the input processing, the user packets (stemming from Transport Streams, Generic Streams, IP streams etc.) are transformed into an appropriately formatted bitstream which is then encoded and mapped on the physical layer resources. The input processing transforms user packets into baseband frames. The term “user packets” used for this invention covers also the case of continuous streams where no packet boundaries existed or are indicated.
The basic data structure at the physical layer is known as a baseband frame. The input stream of digital broadcast data is encapsulated into baseband frames, By applying forward error correction (FEC) to those baseband frames, FEC frames are formed. Baseband frames have a length which depends on the applied coding rate of the FEC coding. Baseband frames together with the parity bytes build FEC frames of fixed length, for instance, of 16,200 or 64.800 bits.
FIG. 1A illustrates the format of a baseband frame 101 with length 102 of bits. The baseband frame 101 comprises a baseband frame header 110 of length 111 (80 bits in DVB-S2, DVB-T2 and DVB-C2), a data field 120 with a data field length 121, and a padding field 130 with length 131. The padding field 130 may include in-band signalling information or be replaced by in-band signalling information. The length 121 of the data field is signalled within the baseband frame header 110. Signalling of the data field length (DFL) indicator 270 (cf. FIG. 2) is necessary in order to distinguish between the data (payload) 120 transported in the baseband frame 101 and padding field 130, which may be carried within the same baseband frame 101. The length 102 of the baseband frame 101 corresponds to the number of bits Kbch to which the BCH code is applied. The padding field 130 has a length of Kbch-DFL-80 bits, wherein the 80 bits correspond to the length 111 of the baseband frame header.
Baseband frames carry the user content data and the meta-data belonging to a particular physical layer pipe of the broadcasting system. The baseband frames encapsulate arbitrary user packets, such as packets carrying data coded with a compression standard such as Moving Picture Experts Group (MPEG)-2 or MPEG-4 part 10 (H.264) and encapsulated into an MPEG transport stream, or any other packets. Moreover, the baseband frames also carry meta-data related to the content carried in the same baseband frame. In other words, baseband frames are the outer content encapsulation entity to which the energy dispersal scrambling as well as physical layer error correction coding is applied. A sequence of the baseband frames builds the content of a physical layer pipe within the broadcasting system.
A forward error correction (FEC) frame 105 is illustrated in FIG. 1B. The forward error correction frame 105 has a length 106 of Nldpc bits, and includes a baseband frame 101 with length 102 of Kbch bits, a field 140 with a length 141 for BCH code parity bits, and a field 150 with a length 151 for parity bits of the Low Density Parity Check (LDPC) code. In the above notation, the subscript (“ldpc” or “bch”) denotes the error correction method applied, N denotes the length of data in bits after applying the method in subscript, and K denotes the length of data in bits to which the subscript method is to be applied. Accordingly, the length 141 of the LDPC parity bit field 140 corresponds to Nbch−Kbch bits. The baseband frame 101 together with the BCH parity bits 140 have a length 161 of Kldpc bits to which the LDPC code is applied which corresponds to Nbch bits of the BCH-encoded data. The length 151 of the LDPC parity bit field 150 thus corresponds to Nldpc−Kldpc bits.
FIG. 2 illustrates a baseband frame header 201 of a normal mode and a baseband frame header 202 of a high efficiency mode defined in the DVB-T2 and -C2 specifications. DVB-S2 uses only one baseband frame format that is identical to the normal mode format in -T2 and -C2 apart from the mode indication that is EXORed with the CRC-8 field in the C2 and T2 cases.
The baseband frame header 201, 202 in normal mode and/or in high-efficiency mode includes the flowing fields.
TS/GS Indicator 210
A TS/GS indicator 210 is an input stream format indicator indicating the format of the input stream transported by the baseband frame. The name “TS/GS” of the indicator is derived from the differentiation between a transport stream (TS) or a generic stream (GS). The length of the TS/GS indicator 210 is two bits for distinguishing the following input stream formats: a generic fixed-length packetized stream (GFPS), a transport stream (TS), a generic continual stream (GCS), and a generic encapsulated stream (GSE: generic stream encapsulation).
SIS/MIS Indicator 220
A SIS/MIS indicator 220 of one-bit length is for indicating whether a single input stream (SIS) or multiple input streams (MIS) are carried within the broadcast signal.
CCM/ACM Indicator 225
A CCM/ACM indicator 225 of one-bit length is for indicating whether constant coding and modulation (CCM) or adaptive coding and modulation (ACM) is applied. If constant coding and modulation is applied, all physical layer pipes use the same coding and modulation scheme. On the other side, if variable coding and modulation is applied, then in each physical layer pipe the modulation and coding scheme may be configured and it then remains constant during transmission. It may be statically reconfigured. In short, the configuration of whether CCM or ACM is applied is not changed frequently.
ISSYI 230
An ISSYI 230 is an input stream synchronization indicator of a one-bit length for indicating whether input stream synchronisation is active, i.e. whether an ISSY (input stream synchronization) field shall be computed and inserted into the baseband frame header in the case of high efficiency mode (ISSY 231 and/or 232) or attached to each user packet (with known packet boundaries) in the case of normal mode.
NPD Indicator 240
An null packet deletion (NPD) indicator 240 is of one-bit length for indicating whether the null packet deletion is activated or not. If null packet deletion is activated, then the number of deleted null packets is computed and appended after the user packets in a field of 8 bits.
EXT Field 245
An extension (EXT) field 245 is media specific and in DVB-T2 it is normally set to zero and reserved for future use.
ISI 250
An input stream identifier (ISI) 250 has a length of one byte. This field of header is denoted as MATYPE-2. It carries ISI if the SIS/MIS indicator is set to one, i.e., to a multiple input stream (MIS). If the SIS/MIS indicator is set to zero, i.e. indicates a single input stream, then the MATTYPE-2 byte is reserved for future use.
UPL Indicator 260
A user packet length indicator (UPL) 260 has a length of 16 bits and indicates user packet length in bits. UPL is not present in the high-efficiency mode.
DFL Indicator 270
The DFL indicator 270 is a data field length indicator of 16-bits length for indicating the data field length 121 in bits of the baseband frame.
SYNC Indicator 280
A synchronization sequence (SYNC) indicator 280 is of 8 bits and not present in the high-efficiency mode. It is not used in generic continuous stream mode and copies a user packet synchronisation byte otherwise.
SYNCD Indicator 285
A SYNCD indicator 285 of 16 bits is for indicating a distance in bits from the beginning of the data field 120 to the first user packet in the data field.
CRC-8/MODE Indicator 290
A CRC-8/MODE indicator 290 of 8-bits length is for carrying error detection parity bits for the baseband frame header and for indicating the BBF mode, i.e. either high efficiency or normal mode.
The first byte of the baseband frame header 201, 202 including TS/GS (2 bits), SIS/MIS (1 bit), CCM/ACM (1 bit), ISSYI (1 bit), NPD (1 bit) and EXT (2 bits) fields is typically denoted as MATYPE-1 byte.
In the high-efficiency mode, the baseband frame header 202 differs from the baseband frame header 201 in the normal mode in that it does not carry the UPL indicator 260 and the synchronization byte SYNC indicator 280. Instead, the baseband frame header 202 can carry in the corresponding positions an ISSY field 231, 232 (input stream synchronization) of 24 bits. In the normal mode, the ISSY field is appended to user packets for packetized streams. In the high efficiency mode. ISSY is transmitted per baseband frame in the baseband frame header, since the user packets of a baseband frame travel together, and therefore experience the same delay/jitter. The high efficiency mode in the DVB-T2 standard can thus be seen as a first attempt towards a more efficient transport of user packets by moving particular parameters from the user packet headers to the baseband frame headers.
With the concept of physical layer pipes, some parameters included in the baseband frames are already indicated by the layer 1 signalling or could be derived from the layer 1 signalling. Indicating the same information on different levels of mapping reduces the efficiency of transmission resources utilisation. Moreover, inconsistencies may arise such as opposite settings for the same parameter having an equivalent, for instance, on both layer 1 signalling and signalling within the baseband frame headers.